An 8-in-diameter grinding wheel rotates at a surface speed of 4000 ft/min in a surface grinding job performed on a flat piece of 4340 steel with hardness = 325 BHN. There are 300 active grits/in2 of wheel surface, and the operation is performed dry. Infeed = 0.0015 in per pass, crossfeed (transverse feed) = 0.20 in, and the reciprocating speed of the work is 30 ft/min. Determine (a) length of contact between the wheel and the work, (b) volume rate of metal removed, (c) number of chips formed per unit time, and (d) average volume per chip? (e) If the tangential cutting force on the workpiece = 23 lb., what is the specific energy U calculated for this job?

A3-mm-thick panel of aluminum alloy (k 177 w/m-k, c 875 j/kg-k and ? = 2770 kg/m) is finished on both sides with an epoxy coating that must be cured at or above t,-150°c for at least 5 min. the production line for the curing operation involves two steps: (1) heating in a large oven with air at ts,0-175°c and a convection coefficient of h, 40 w/m2. k, and (2) cooling in a large chamber with air at 25°c and a con- vection coefficient of he 10 w/m2.k. the heating portion of the process is conducted over a time interval te which exceeds the ime required to reach 150°c by 5 min (h = r + 300 s). the coating has an emissivity of ? = 0.8, and the temperatures of the oven and chamber walls are 175 and 25°c, respectively. if the panel is placed in the oven at an initial temperature of 25°c and removed from the chamber at a safe-to-touch tempera ture of 37°c, what is the total elapsed time for the two-step curing operation?